POS1020 A DIMINISHED EXPRESSION OF THE UBIQUITIN-PROTEASOME SYSTEM IN PATIENTS WITH RHEUMATOID ARTHRITIS AND DIABETES IS LINKED TO IL-1 PATHWAY HYPER-ACTIVITY
Authors: P. Ruscitti, D. Currado, F. Rivellese, M. Vomero, L. Navarini, P. Cipriani, C. Pitzalis, R. Giacomelli
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> A consistent connection between rheumatoid arthritis (RA) and type 2 diabetes (T2D) has been recently reported highlighting interleukin-1β (IL-1β) as shared pathogenic pathway and therapeutic target [1]. In a clinical trial enrolling patient with RA and T2D, we demonstrated that IL-1 inhibition led to a marked reduction of glycated haemoglobin together with a decrease of RA disease activity [2]. <h3>Objectives</h3> To evaluate the synovial expression of IL-1 related genes and the relationship to the ubiquitin-proteasome system in the synovial tissues of RA patients with and without T2D. To assess the effects of high concentration of insulin in vitro, mimicking the hyperinsulinism of the early phases of T2D, on ubiquitinated proteins in fibroblast-like synoviocytes (FLSs). <h3>Methods</h3> Early (&lt;1 year) treatment-naïve RA patients with T2D (RA/T2D n=16) were compared with age- and gender-matched RA patients without T2D (n=16) enrolled in the Pathobiology of Early Arthritis Cohort (PEAC) [3]. Synovial tissue biopsies obtained under ultrasound guidance underwent RNA-sequencing as previously described [3], and we compared IL-1 pathway genes in patients without and with T2D. The synovial expression of ubiquitin in macrophages and synovial lining fibroblasts was assessed by immunohistochemistry/immunofluorescence and correlated with synovial pathotypes [4]. Finally, FLSs from RA patients (n=5) were isolated and treated with human insulin (200 and 500 nM) and ubiquitinated proteins were assessed by western blot. <h3>Results</h3> Synovial RNA-sequencing showed that one third of IL-1 pathway genes (41/138) were significantly different in RA/T2D patients compared to RA patients without T2D. In parallel, synovial tissues of RA/T2D patients were characterised by a consistent reduced expression of ubiquitin-proteasome genes. More specifically, ubiquitin genes (<i>UBB</i>, <i>UBC</i>, and <i>UBA52</i>) were significantly lower in T2D/RA patients. Furthermore, 22 genes codifying proteasome subunits were significantly lower in RA/T2D patients (<i>PSMA2</i>, <i>PSMA6</i>, <i>PSMA7</i>, <i>PSMB1, PSMB3, PSMB4, PSMB6, PSMB7, PSMB8, PSMB9, PSMB10</i>, <i>PSMC1, PSMC3, PSMC5, PSMC13</i>, <i>PSMD4, PSMD7, PSMD8, PSMD9</i>, <i>PSME1, PSME2</i>, and <i>PSMF1</i>). Additionally, several genes regulating ubiquitin and proteasome system were significantly different in the synovial tissue of RA/T2D patients. Specifically, <i>APP</i>, <i>BAG4</i>, and <i>BTRC</i> were upregulated in RA/T2D patients. Conversely, <i>RACK1</i>, <i>RBX1</i>, <i>RPS27A</i>, <i>SEM1</i>, <i>SHARPIN</i>, and <i>SIGIRR</i> were significantly downregulated in RA/T2D patients. Immunohistochemistry showed a significant reduction of the percentage of ubiquitin-positive cells in synovial tissues of RA/T2D patients. The percentage of ubiquitin-positive cells was also increased in patients with a lympho-myeloid pathotype compared to diffuse myeloid or pauci-immune-fibroid. Despite its widespread expression in synovia, immunofluorescence showed that ubiquitin mainly colocalized with synovial macrophages and lining fibroblasts. Finally, <i>in vitro</i> experiments showed a reduction of ubiquitinated proteins in RA-FLSs treated with a high concentration of insulin (500 nM). <h3>Conclusion</h3> Increased IL-1 gene expression was observed in the synovial tissues of RA/T2D patients linked with decreased ubiquitin-proteasome system. These findings may provide a mechanistic explanation of the observed clinical benefits of IL-1 inhibition in patients with RA and concomitant comorbid T2D, as the reduction of the ubiquitin-proteasome system may enhance the levels of precursor IL-1β and the production of bioactive IL-1β. <h3>References</h3> [1] Giacomelli R, et al. Expert Rev Clin Immunol. 2016;12:849-55 [2] Ruscitti P, et al. PLoS Med. 2019;16:e1002901 [3] Lewis MJ, et al. Cell Rep. 2019;28:2455-70 [4] Humby F, et al. Ann Rheum Dis. 2019;78:761-72 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.